Shelf Circulation Induced by an Orographic Wind Jet

Abstract

The dynamical response to cross‐shelf wind‐jet episodes is investigated. The study area is located at the northern margin of the Ebro Shelf, in the Northwestern (NW) Mediterranean Sea, where episodes of strong northwesterly wind occur. In this case, the wind is channeled through the Ebro Valley and intensifies upon reaching the sea, resulting in a wind jet. The wind‐jet response in terms of water circulation and vertical density structure is investigated using a numerical model. The numerical outputs agree with water current observations from a high‐frequency radar. Additionally, temperature, sea level, and wind measurements are also used for the skill assessment of the model. For the wind‐jet episodes, the numerical results show a well‐defined two‐layer circulation in the cross‐shelf direction, with the surface currents in the direction of the wind. This pattern is consistent with sea level set‐down due to the wind effect. The comparison of the vertical structure response for different episodes revealed that the increase of stratification leads to an onshore displacement of the transition from inner shelf to mid‐shelf. In general, the cross‐shelf momentum balance during a wind‐jet episode exhibits a balance between the frictional terms and the pressure gradient in shallow waters, shifting to a balance between the Coriolis force and the wind stress terms in deeper waters.

Wave–Current Interactions in a Wind-jet Region

“…In addition, the region affected by the wind jet seems to be expanded to the northeast, resulting in stronger water currents in the cRS run. Nevertheless, the main current patterns obtained with both runs are very similar and coincide with the behavior presented in Ràfols et al (2017a).…”

“…The predominant regional current is the quasipermanent slope current known as the Northern Current, which is an entity flowing along the continental slope (Millot, 1999) that can be modified by mesoscale events such as current meandering or eddies (Font et al, 1995). The water circulation in the inner and mid-shelf presents strong temporal and spatial variability due to the strong gradients in the bathymetry and wind field associated with wind-jet episodes (Grifoll et al, 2015;Ràfols et al, 2017a). The wave climate at the Ebro Delta is characterized by the predominance of NW winds (which coincides with the predominance of NW winds), although there are also significant storms from the east and south.…”

“…This region is very interesting from a meteo-oceanographic point of view because multiple processes take place, such as bimodal wave spectra and the development of a two-layer cross-shelf flow. Some authors have investigated the circulation patterns (Grifoll et al, 2015;Ràfols et al, 2017a) and the wave field (Bolaños-Sanchez et al, 2007;Grifoll et al, 2016;Ràfols et al, 2017b) during these NW wind-jet events but less efforts have been made at investigating the WCI in the region. Due to the limited observational data, in order to study the wind-jet induced dynamics of the region, the use of numerical models is required.…”

“…The selected study period is from March 15 2014 to May 15 2014 because it contains four wind-jet episodes. Additionally, this period has been previously used to validate numerical models in the study region and the wind-wave characterization (Ràfols et al, 2017b), and water shelf circulation (Ràfols et al, 2017a) was investigated by combining numerical efforts and in situ observations. This work is organized as follows.…”

The land–sea coastal border: a quantitative definition by considering the wind and wave conditions in a wave-dominated, micro-tidal environment

“…Such a non-structured-grid approach avoids nesting and internal boundary conditions, while maintaining a good spatial resolution to capture bottom and coastline irregularity (submarine canyons and capes or pro-deltas that are found in the Catalan continental shelf). Furthermore, unstructured meshes are well suited to tackle non-linear effects (Qi et al, 2009;Roland et al, 2012;Roland and Ardhuin, 2014). The resulting wave fields have been validated with two directional wave buoys at the northern (Begur, deployed at 1200 m) and southern (Tarragona coastal buoy, deployed at 15 m) ends of the domain, managed by Puertos del Estado (Fig.…”